As pointed out in U.S. Pat No. 3,881,889 (commonly owned herewith), dimensional relationships and closeness of tolerances are extremely important in the design and manufacture of certain cutting tools, such as those used with gear cutting machinery capable of generating tooth profiles for spiral, bevel, hypoid, and other types of gears. The geometry of cutting blades for such machinery has been relatively complex in order to accomodate geometric changes which may be desired or required in the finished gear products. As a result of these special requirements, for cutting tools of this type, there has been a long history of manufacture and usage of cutting tools which are relatively complex and costly in terms of design and ease of manufacture.
Recently, there have been efforts to simplify the geometry and design of cutting blades used in gear cutting applications, and applicants herein have themselves filed U.S. Application Ser. No. 812,197 on July 5, 1977 on the subject of an improved method for resharpening such cutting blades. That same application discloses apparatus for carrying out the claimed method, and this present application is directed to a disclosure of specific apparatus being designed and built by The Gleason Works, Rochester, N.Y. for carrying out high production sharpening and resharpening of various forms of cutting blades and other tools. Although this invention is directed primarily to the special problems of maintaining critical tolerances and relationships in cutting tools designed for spiral, bevel, and hypoid gears, it should be appreciated that the apparatus disclosed herein may be used to produce cutting tools for other forms of gears (such as spur and helical gears) and additionally may be used for sharpening and resharpening cutting tools used for milling or other stock removal applications.
Various forms of equipment have been designed for carrying out specialized grinding operations for sharpening tooling for machines. For example, it is known to provide for a swinging motion of a tool relative to a grinding wheel so as to produce a preferred end configuration on the tool. Patents disclosing this general concept appear to be directed primarily to methods and apparatus for sharpening drill bits in which a conical end profile is required for each drill bit, as exemplified in U.S. Pat. Nos. 2,471,443; 3,535,831; 3,656,264; and 3,838,540.
It is also known to provide for batch grinding of relatively simple cutting blades designed for use in gear cutting applications, as shown in U.S. Pat. Nos. 2,367,494 and 3,487,592. These types of grinding, and the tooling being ground or resharpened, are closely related to the specific subject matter of the present invention inasmuch as the intent here is to provide production apparatus for precision grinding a plurality of gear cutting blades. However, as far as is known by applicants herein, prior art efforts to resharpen precision cutting blades have not fully satisfied the production requirements of major users of gear cutting machinery. For one reason or another the types of equipment which have been tried require unacceptably long periods of time for changing blade batches and do not appear to offer full dimensional control over a range of blade profiles to be sharpened in a precision production process. Accordingly, it is believed that the apparatus described and claimed herein represents an improvement over prior art efforts in this field.
In accordance with the present invention all critical surfaces of cutting blades are formed and established in what amounts to a single grinding plane of a grinding wheel. This single grinding plane may be considered a flat plane for many typical grinding operations contemplated herein, but it is also intended that the terminology "single grinding plane" include grinding wheel surfaces which have been shaped to produce special profiles on cutting blades. In contrast to what will be described herein as a "single grinding plane", the grinding equipment illustrated in U.S. Pat. No. 3,881,889 (commonly owned herewith) requires the use of separate grinding planes 66 and 68 (FIGS. 7 through 11 thereof) of a grinding wheel in order to carry out all steps of resharpening of a cutting blade of the type shown. Grinding wheels which are designed and manufactured with multiple grinding planes are far more costly to purchase and more difficult to maintain than grinding wheels of simpler design which include only a single grinding plane for carrying out all operations. In order to take advantage of a single grinding plane, however, it is necessary to provide apparatus which can orient a batch of cutting blades into different positions relative to the single plane of the grinding wheel. The present invention does this with an arrangement of tool-holding equipment which permits set-up of the machine with only a single reference axis for determining initial and all subsequent positions of a batch of tools relative to the single grinding plane. Thus, the basic approach of the present invention is a significant one inasmuch as it permits the use of simpler and less costly grinding wheels and dressers for establishing critical relationships on cutting blades.
As pointed out in the parent application Ser. No. 812,197, mentioned above, it is important that certain relationships be established between individual cutting blades to be sharpened and the single grinding plane of a grinding wheel. In addition, it is important in grinding operations of this type, which necessarily involve a series of steps of separate grinding contacts with a grinding surface, to precisely locate each surface being ground with reference to other surfaces which were previously ground or which will be subsequently ground. Maintenance of correct relationships, and even knowing precisely where a workpiece is located at all times relative to a grinding surface, become more difficult as more and more workpieces are introduced into each grinding cycle. Thus, the problems of correctly relating a single cutting blade to a grinding surface become greatly increased when a plurality of cutting blades are being handled at the same time. The apparatus of this invention solves these problems, and additionally, offers higher production rates than have been achieved heretofore for cutting blades and other tooling of this type.
In its broadest form the apparatus of the present invention comprises a machine having a base structure, a grinding wheel assembly mounted at one end of the base structure, and a cradle assembly mounted at an opposite end of the base structure. Preferrably the base has an inclined upper surface for supporting essential components of the machine, and this permits mounting of the grinding wheel assembly at a lower level of the surface for movement towards and away from the mounted position of a plurality of cutting blades carried by the cradle assembly at an upper level of the base structure. The cutting blades are secured in a tool-holding means which permits orientation of common selected surfaces of all of the cutting blades toward the grinding plane of the grinding wheel. In its preferred embodiment the tool-holding means comprises a ring-shaped member mounted on a drive spindle contained within the cradle assembly so that a plurality of blades can be spun relative to the grinding plane of the grinding wheel for rapidly resharpening a selected surface of all of the blades in any given orientation of the blades to the grinding wheel plane.
Considering the invention in a specific form in which it will be initially manufactured, it is intended that certain types of cutting blades be handled by applicants' machine. These blades are of a type which include at least (a) a first side relief surface, (b) a topland surface, (c) a curved surface interconnecting the first side relief surface and the topland surface, and (d) a second side relief surface, (as disclosed in U.S. Pat. No. 3,881,889 and in commonly owned application Ser. No. 741,837, filed on Nov. 15, 1976, now U.S. Pat. No. 4,060,881 by Ryan and Thomas, for example). Certain forms of these blades may additionally include a curved surface interconnecting the topland surface and the second side relief surface. Cutting blades of this type have protected front (or chip) faces which do not require resharpening. A preferred machine for sharpening blades of this type includes a tool-holding ring for carrying a plurality of blades with their end portions projecting beyond a circumference thereof, a driving means for spinning the tool-holding ring relative to a grinding wheel, a cradle assembly for supporting the tool-holding ring in separate positons for grinding the cutting blade surfaces (a)-(d) and in the same grinding plane and area of the grinding wheel, and control means for moving the cradle assembly to the separate positions. One of the features of the apparatus is its provision for turning a cradle body portion of cradle assembly over to a position in which opposite sides of a plurality of cutting blades can be ground as the tool-holding ring spins the blades in contact with the grinding wheel. This is accomplished with means for turning the cradle body and its contained tool-holding ring over in a cradle axis and this further requires a drive train for maintaining driving contact between a drive motor and the tool-holding ring for all positions in which the cradle body may be turned for grinding opposite surfaces of the cutting blades. Additionally, a separate cradle base of the cradle assembly is provided with a pivotal mounting relative to the base structure of the machine so that the cradle assembly can be swung about a reference axis which is used to establish correct positioning of the cutting blades relative to the grinding plane and to provide for generation of curved surfaces interconnecting the side relief surfaces and the top-land surfaces of the cutting blades. Adjustment features are included to provide for a full range of positions of different shapes of cutting tools relative to the reference axis and grinding plane for the machine.
Thus, the present invention offers specialized equipment for carrying out the basic method of resharpening described in U.S. Pat. No. 3,881,889 and the specific method described in co-pending U.S. Application Ser. No. 812,197. These methods can be carried out at high production rates and with complete control of dimensional and geometric relationships of the cutting blades being sharpened. As a result, greater productivity (and therefore lower cost) of manufacturing can be achieved with the specialized grinding equipment of this invention.
These and other features and advantages of the invention will become apparent in the more detailed discussion that follows, and in that discussion reference will be made to the accompanying drawings as briefly described below.